Macrotubule-dependent protoplast volume regulation in plasmolysed root-tip cells of Triticum turgidum: involvement of phospholipase D

Some like it cold: The cellular organization and physiological limits of cold-tolerant nitrite-oxidizing Nitrotoga

Chemolithoautotrophic production of nitrate is accomplished by the polyphyletic functional group of nitrite-oxidizing bacteria (NOB). A widely distributed and important NOB clade in nitrogen removal processes at low temperatures is Nitrotoga, which however remains understudied due to the scarcity of cultivated representatives. Here, we present physiological, ultrastructural and genomic features of Nitrotoga strains from various habitats, including the first marine species enriched from an aquaculture system. Immunocytochemical analyses localized the nitrite-oxidizing enzyme machinery in the wide irregularly shaped periplasm, apparently without contact to the cytoplasmic membrane, confirming previous genomic data suggesting a soluble nature. Interestingly, in two strains we also observed multicellular complexes with a shared periplasmic space, which seem to form through incomplete cell division and might enhance fitness or survival. Physiological tests revealed differing tolerance limits towards dissolved inorganic nitrogen concentrations and confirmed the generally psychrotolerant nature of the genus was. Moreover, comparative analysis of 15 Nitrotoga genomes showed, e.g., a unique gene repertoire of the marine strain that could be advantageous in its natural habitat and confirmed the lack of genes for assimilatory nitrite reduction in a strain found to require ammonium for growth. Overall, these novel insights largely broaden our knowledge of Nitrotoga and elucidate the metabolic variability, physiological limits and thus potential ecological roles of this group of nitrite oxidizers. This article is protected by copyright. All rights reserved.

Microtubule organization changes severely after mannitol and n-butanol treatments inducing microspore embryogenesis in bread wheat

BACKGROUND

A mannitol stress treatment and a subsequent application of n-butanol, known as a microtubule-disrupting agent, enhance microspore embryogenesis (ME) induction and plant regeneration in bread wheat. To characterize changes in cortical (CMT) and endoplasmic (EMT) microtubules organization and dynamics, associated with ME induction treatments, immunocytochemistry studies complemented by confocal laser scanning microscopy (CLSM) were accomplished. This technique has allowed us to perform advanced 3- and 4D studies of MT architecture. The degree of MT fragmentation was examined by the relative fluorescence intensity quantification.

RESULTS

In uni-nucleated mannitol-treated microspores, severe CMT and EMT fragmentation occurs, although a complex network of short EMT bundles protected the nucleus. Additional treatment with n-butanol resulted in further depolymerization of both CMT and EMT, simultaneously with the formation of MT aggregates in the perinuclear region. Some aggregates resembled a preprophase band. In addition, a portion of the microspores progressed to the first mitotic division during the treatments. Bi-nucleate pollen-like structures showed a high MT depolymerization after mannitol treatment and numerous EMT bundles around the vegetative and generative nuclei after n-butanol. Interestingly, bi-nucleate symmetric structures showed prominent stabilization of EMT.

CONCLUSIONS

Fragmentation and stabilization of microtubules induced by mannitol- and n-butanol lead to new configurations essential for the induction of microspore embryogenesis in bread wheat. These results provide robust insight into MT dynamics during EM induction and open avenues to address newly targeted treatments to induce ME in recalcitrant species.

Quartz Crystal Microbalance with Dissipation Monitoring of Dynamic Viscoelastic Changes of Tobacco BY-2 Cells under Different Osmotic Conditions

The plant cell mechanics, including turgor pressure and wall mechanical properties, not only determine the growth of plant cells, but also reflect the functional and structural changes of plant cells under biotic and abiotic stresses. However, there are currently no appropriate techniques allowing to monitor the complex mechanical properties of living plant cells non-invasively and continuously. In this work, quartz crystal microbalance with dissipation (QCM-D) monitoring technique with overtones (3-9) was used for the dynamic monitoring of adhesions of living tobacco BY-2 cells onto positively charged N,N-dimethyl-N-propenyl-2-propen-1-aminiumchloride homopolymer (PDADMAC)/SiO2 QCM crystals under different concentrations of mannitol (CM) and the subsequent effects of osmotic stresses. The cell viscoelastic index (CVIn) (CVIn = ΔD⋅n/ΔF) was used to characterize the viscoelastic properties of BY-2 cells under different osmotic conditions. Our results indicated that lower overtones of QCM could detect both the cell wall and cytoskeleton structures allowing the detection of plasmolysis phenomena; whereas higher overtones could only detect the cell wall's mechanical properties. The QCM results were further discussed with the morphological changes of the BY-2 cells by an optical microscopy. The dynamic changes of cell's generated forces or cellular structures of plant cells caused by external stimuli (or stresses) can be traced by non-destructive and dynamic monitoring of cells' viscoelasticity, which provides a new way for the characterization and study of plant cells. QCM-D could map viscoelastic properties of different cellular structures in living cells and could be used as a new tool to test the mechanical properties of plant cells.

Salt Stress-Induced Structural Changes Are Mitigated in Transgenic Tomato Plants Over-Expressing Superoxide Dismutase

Various abiotic stresses cause the appearance of reactive oxygen species (ROS) in plant cells, which seriously damage the cellular structures. The engineering of transgenic plants with higher production of ROS-scavenging enzyme in plant cells could protect the integrity of such a fine intracellular structure as the cytoskeleton and each cellular compartment. We analyzed the morphological changes in root tip cells caused by the application of iso-osmotic NaCl and Na2SO4 solutions to tomato plants harboring an introduced superoxide dismutase gene. To study the roots of tomato plants cultivar Belyi Naliv (WT) and FeSOD-transgenic line, we examined the distribution of ROS and enzyme-linked immunosorbent detection of α-tubulin. In addition, longitudinal sections of the root apexes were compared. Transmission electronic microscopy of atypical cytoskeleton structures was also performed. The differences in the microtubules cortical network between WT and transgenic plants without salt stress were detected. The differences were found in the cortical network of microtubules between WT and transgenic plants in the absence of salt stress. While an ordered microtubule network was revealed in the root cells of WT tomato, no such degree of ordering was detected in transgenic line cells. The signs of microtubule disorganization in root cells of WT plants were manifested under the NaCl treatment. On the contrary, the cytoskeleton structural organization in the transgenic line cells was more ordered. Similar changes, including the cortical microtubules disorganization, possibly associated with the formation of atypical tubulin polymers as a response to salt stress caused by Na2SO4 treatment, were also observed. Changes in cell size, due to both vacuolization and impaired cell expansion in columella zone and cap initials, were responsible for the root tip tissue modification.

The p38-like MAP kinase modulated H2O2 accumulation in wounding signaling pathways of sweet potato

In sweet potato (Ipomoea batatas cv Tainung 57), MAPK cascades are involved in the regulation of Ipomoelin (IPO) expression upon wounding. p38 MAPK plays an important role in plant's responses to various environmental stresses. However, the role of p38-like MAPK in wounding response is still unknown. In this study, the levels of phosphorylated-p38-like MAPK (pp38-like MAPK) in sweet potato were noticeably reduced after wounding. In addition, SB203580 (SB), a specific inhibitor blocking p38 MAPK phosphorylation, considerably decreased the accumulation of pp38-like MAPK. Expression of a wound-inducible gene IPO was elevated by SB. Moreover, it stimulated hydrogen peroxide (H₂O₂) production rather than cytosolic Ca²⁺ elevation in sweet potato leaves. However, NADPH oxidase (NOX) inhibitor diphenyleneiodonium could not inhibit IPO induction stimulated by SB. These results indicated a p38-like MAPK mechanism was involved in the regulation of IPO expression through NOX-independent H₂O₂ generation. In addition, the presence of the protein phosphatase inhibitor okadaic acid or the MEK1/ERK inhibitor PD98059 repressed the H₂O₂- or SB-induced IPO expression, demonstrating phosphatase(s) and MEK1/ERK functioning in the downstream of H₂O₂ and pp38-like MAPK in the signal transduction pathway stimulating IPO. Conclusively, wounding decreased the amount of pp38-like MAPK, stimulated H₂O₂ production, and then induced IPO expression.

Plasmolysis: Loss of Turgor and Beyond

Plasmolysis is a typical response of plant cells exposed to hyperosmotic stress. The loss of turgor causes the violent detachment of the living protoplast from the cell wall. The plasmolytic process is mainly driven by the vacuole. Plasmolysis is reversible (deplasmolysis) and characteristic to living plant cells. Obviously, dramatic structural changes are required to fulfill a plasmolytic cycle. In the present paper, the fate of cortical microtubules and actin microfilaments is documented throughout a plasmolytic cycle in living cells of green fluorescent protein (GFP) tagged Arabidopsis lines. While the microtubules became wavy and highly bundled during plasmolysis, cortical filamentous actin remained in close vicinity to the plasma membrane lining the sites of concave plasmolysis and adjusting readily to the diminished size of the protoplast. During deplasmolysis, cortical microtubule re-organization progressed slowly and required up to 24 h to complete the restoration of the original pre-plasmolytic pattern. Actin microfilaments, again, recovered faster and organelle movement remained intact throughout the whole process. In summary, the hydrostatic skeleton resulting from the osmotic state of the plant vacuole "overrules" the stabilization by cortical cytoskeletal elements.

Phosphorylation of a p38-like MAPK is involved in sensing cellular redox state and drives atypical tubulin polymer assembly in angiosperms

Reactive oxygen species (ROS) imbalance is a stressful condition for plant cells accompanied by dramatic changes in tubulin cytoskeleton. Here, evidence is provided that alterations in ROS levels directly interfere with the phosphorylation state of a p38-like MAPK in the angiosperms Triticum turgidum and Arabidopsis thaliana. Both oxidative stress generators and chemicals inducing ROS scavenging or decreasing ROS production resulted in the accumulation of a phospho-p46 protein similar to p38-MAPK. Importantly, the rhd2 A. thaliana mutants exhibited a remarkable increase in levels of phospho-p46. The presence of the p38-MAPK inhibitor SB203580 attenuated the response to ROS disturbance, prevented microtubule disappearance and resulted in a dramatic decrease in the number of atypical tubulin polymers. Moreover, in roots treated simultaneously with substances inducing ROS overproduction and others resulting in low ROS levels, phospho-p46 levels and the organization of tubulin cytoskeleton were similar to controls. Collectively, our experimental data suggest, for the first time in plants, that p46 functions as a putative sensor of redox state, the activation of which initiates downstream signalling events leading to microtubule disruption and subsequent assembly of atypical tubulin polymers. Thus, p46 seems to participate in perception of ROS homeostasis disturbance as well as in cellular responses to redox imbalance.

The interplay between ROS and tubulin cytoskeleton in plants

Plants have to deal with reactive oxygen species (ROS) production, since it could potentially cause severe damages to different cellular components. On the other hand, ROS functioning as important second messengers are implicated in various developmental processes and are transiently produced during biotic or abiotic stresses. Furthermore, the microtubules (MTs) play a primary role in plant development and appear as potent players in sensing stressful situations and in the subsequent cellular responses. Emerging evidence suggests that ROS affect MTs in multiple ways. The cellular redox status seems to be tightly coupled with MTs. ROS signals regulate the organization of tubulin cytoskeleton and induce tubulin modifications. This review aims at summarizing the signaling mechanisms and the key operators orchestrating the crosstalk between ROS and tubulin cytoskeleton in plant cells. The contribution of several molecules, including microtubule associated proteins, oxidases, kinases, phospholipases, and transcription factors, is highlighted.

Regulation of cytoskeletal dynamics by phospholipase D and phosphatidic acid

Plants respond to diverse biotic and abiotic stimuli as well as to endogenous developmental cues. Many of these stimuli result in altered activity of phospholipase D (PLD), an enzyme that hydrolyzes structural phospholipids producing phosphatidic acid (PA). PA is a key signaling intermediate in animals, but its targets in plants are relatively uncharacterized. Recent studies have demonstrated that the cytoskeleton is a major target of PLD-PA signaling and identified a positive feedback loop between actin turnover and PLD activity. Moreover, two cytoskeletal proteins, capping protein and MAP65-1, have been identified as PA-binding proteins regulating actin and microtubule organization and dynamics. In this review, we highlight the role of the PLD-PA module as an important hub for housekeeping and stress-induced regulation of membrane-associated cytoskeletal dynamics.

Microtubules, signalling and abiotic stress

Plant microtubules, in addition to their role in cell division and axial cell expansion, convey a sensory function that is relevant for the perception of mechanical membrane stress and its derivatives, such as osmotic or cold stress. During development, sensory microtubules participate in the mechanical integration of plant architecture, including the patterning of incipient organogenesis and the alignment with gravity-dependent load. The sensory function of microtubules depends on dynamic instability, and often involves a transient elimination of cortical microtubules followed by adaptive events accompanied by subsequent formation of stable microtubule bundles. It is proposed that microtubules, because of their relative rigidity in combination with their innate nonlinear dynamics, are pre-adapted for a function as mechanosensors and, in concert with the flexible actin filaments and the anisotropic cell wall, comprise a tensegral system that allows plant cells to sense geometry and to respond to fields of mechanical strains such that the load is minimized. Microtubules are proposed as elements of a sensory hub that decodes stress-related signal signatures, with phospholipase D as an important player.

α-tubulin is rapidly phosphorylated in response to hyperosmotic stress in rice and Arabidopsis

By using high-resolution two-dimensional PAGE followed by phosphoprotein-specific staining and peptide mass fingerprint analysis along with other assays, we found that α-tubulin is phosphorylated in response to hyperosmotic stress in rice and Arabidopsis. The onset of the phosphorylation response was as early as 2 min after hyperosmotic stress treatment, and a major proportion of α-tubulin was phosphorylated after 60 min in root tissues. However, the phosphorylated form of α-tubulin was readily dephosphorylated upon stress removal. The phosphorylation site was identified as Thr349 by comprehensive mutagenesis of serine/threonine residues in a rice α-tubulin isoform followed by evaluation in cultured cell protoplasts. This residue is located at the surface for the interaction with β-tubulin in polymerized α-β tubulin dimers and has been proposed to be directly involved in this interaction. Thus, α-tubulin phosphorylation was considered to occur on free tubulin dimers in response to hyperosmotic stress. The incorporation of green fluorescent protein (GFP)-α-tubulin into cortical microtubules was completely inhibited in transgenic Arabidopsis when Thr349 was substituted with glutamate or aspartate. Using transgenic Arabidopsis plants expressing GFP-α-tubulin, we found that hyperosmotic stress causes extensive cortical microtubule depolymerization. Microtubule-destabilizing treatments such as propyzamide or oryzalin and temperature stresses resulted in α-tubulin phosphorylation, whereas hyperosmotic stress-induced α-tubulin phosphorylation was partially inhibited by taxol, which stabilizes microtubules. These results and the three-dimensional location of the phosphorylation site suggested that microtubules are depolymerized in response to hyperosmotic stress via α-tubulin phosphorylation. Together, the results of the present study reveal a novel mechanism that globally regulates the microtubule polymerization.

Effects of bisphenol A on the microtubule arrays in root meristematic cells of Pisum sativum L

Bisphenol A (BPA), a widely used chemical in the plastics industry that displays weak oestrogenic properties, is an emerging environmental pollutant, potentially harmful to living organisms. The presumed cytotoxicity of BPA to plant cells has been poorly studied. To understand how BPA might influence plant cell division and affect the underlying cytoskeleton, the effects of BPA on the microtubule (MT) arrays of meristematic root-tip cells of Pisum sativum L. were investigated. Root tips of young seedlings were exposed to 20, 50 and 100mg/L BPA for 1, 3, 6, 12 and 24h. The effects of each treatment were determined by means of confocal laser scanning microscopy after immunolabelling of tubulin and counterstaining of DNA, and by use of light and transmission electron microscopy. It was found that BPA affected normal chromosome segregation, hampered the completion of cytokinesis and deranged interphase and mitotic MT arrays. BPA effects were dependent on the stage of each cell at the time of BPA entrance. Moreover, BPA induced the formation of macrotubules with a mean diameter of 32 ± 0.14 nm, compared with 23 ± 0.70 nm for the MT arrays in untreated cells. Finally, all MT arrays and macrotubules were depolymerised upon longer treatment. Taken together, the data suggest that BPA exerts acute anti-mitotic effects on meristematic root-tip cells of P. sativum, MT arrays constitute a primary sub-cellular target of BPA toxicity, and the manifested chromosomal abnormalities could be attributed to the disruption of the MT cytoskeleton.

Plant cell division: ROS homeostasis is required

Accumulated evidence indicates that ROS fluctuations play a critical role in cell division. Dividing plant cells rapidly respond to them. Experimental disturbance of ROS homeostasis affects: tubulin polymerization; PPB, mitotic spindle and phragmoplast assembly; nuclear envelope dynamics; chromosome separation and movement; cell plate formation. Dividing cells mainly accumulate at prophase and delay in passing through the successive cell division stages. Notably, many dividing root cells of the rhd2 Arabidopsis thaliana mutants, lacking the RHD2/AtRBOHC protein function, displayed aberrations, comparable to those induced by low ROS levels. Some protein molecules, playing key roles in signal transduction networks inducing ROS production, participate in cell division. NADPH oxidases and their regulators PLD, PI3K and ROP-GTPases, are involved in MT polymerization and organization. Cellular ROS oscillations function as messages rapidly transmitted through MAPK pathways inducing MAP activation, thus affecting MT dynamics and organization. RNS implication in cell division is also considered.

Microtubules and the tax payer

Plant microtubules have evolved into a versatile tool to link environmental signals into flexible morphogenesis. Cortical microtubules define the axiality of cell expansion by control of cellulose orientation. Plant-specific microtubule structures such as preprophase band and phragmoplast determine symmetry and axiality of cell divisions. In addition, microtubules act as sensors and integrators for stimuli such as mechanic load, gravity, but also osmotic stress, cold and pathogen attack. Many of these functions are specific for plants and involve specific proteins or the recruitment of proteins to new functions. The review aims to ventilate the potential of microtubule-based strategies for biotechnological application by highlighting representative case studies. These include reorientation of cortical microtubules to increase lodging resistance, control of microtubule dynamics to alter the gravity-dependent orientation of leaves, the use of microtubules as sensitive thermometers to improve adaptive cold tolerance of chilling and freezing sensitive plants, the reduction of microtubule treadmilling to inhibit cell-to-cell transport of plant viruses, or the modulation of plant defence genes by pharmacological manipulation of microtubules. The specificity of these responses is controlled by a great variety of specific associated proteins opening a wide field for biotechnological manipulation of plant architecture and stress tolerance.

Disturbance of reactive oxygen species homeostasis induces atypical tubulin polymer formation and affects mitosis in root-tip cells of Triticum turgidum and Arabidopsis thaliana

In this study, the effects of disturbance of the reactive oxygen species (ROS) homeostasis on the organization of tubulin cytoskeleton in interphase and mitotic root-tip cells of Triticum turgidum and Arabidopsis thaliana were investigated. Reduced ROS levels were obtained by treatment with diphenylene iodonium (DPI) and N-acetyl-cysteine, whereas menadione was applied to achieve ROS overproduction. Both increased and low ROS levels induced: (a) Macrotubule formation in cells with low ROS levels and tubulin paracrystals under oxidative stress. The protein MAP65-1 was detected in treated cells, exhibiting a conformation comparable to that of the atypical tubulin polymers. (b) Disappearance of microtubules (MTs). (c) Inhibition of preprophase band formation. (d) Delay of the nuclear envelope breakdown at prometaphase. (e) Prevention of perinuclear tubulin polymer assembly in prophase cells. (f) Loss of bipolarity of prophase, metaphase and anaphase spindles. Interestingly, examination of the A. thaliana rhd2/At respiratory burst oxidase homolog C (rbohc) NADPH oxidase mutant, lacking RHD2/AtRBOHC, gave comparable results. Similarly to DPI, the decreased ROS levels in rhd2 root-tip cells, interfered with MT organization and induced macrotubule assembly. These data indicate, for first time in plants, that ROS are definitely implicated in: (a) mechanisms controlling the assembly/disassembly of interphase, preprophase and mitotic MT systems and (b) mitotic spindle function. The probable mechanisms, by which ROS affect these processes, are discussed.

Arabidopsis homologs of nucleus- and phragmoplast-localized kinase 2 and 3 and mitogen-activated protein kinase 4 are essential for microtubule organization

A double homozygous recessive mutant in the Arabidopsis thaliana homologs of nucleus- and phragmoplast-localized kinase 2 (ANP2) and 3 (ANP3) genes and a homozygous recessive mutant in the mitogen-activated protein kinase 4 (MPK4) gene of Arabidopsis exhibit deficiencies in the overall microtubule (MT) organization, which result in abnormal cell growth patterns, such as branching of root hairs and swelling of diffusely growing epidermal cells. Genetic, pharmacological, molecular, cytological, and biochemical analyses show that the major underlying mechanism for these phenotypes is excessive MT stabilization manifested in both mutants as heavy MT bundling, disorientation, and drug stability. The above defects in MAPK signaling result in the adverse regulation of members of the microtubule-associated protein (MAP65) protein family, including strongly diminished phosphorylation of MAP65-1. These data suggest that ANP2/ANP3, MPK4, and the microtubule-associated protein MAP65-1, a putative target of MPK4 signaling, are all essential for the proper organization of cortical microtubules in Arabidopsis epidermal cells.

Cerium elicitor-induced phosphatidic acid triggers apoptotic signaling development in Taxus cuspidata cell suspension cultures

Degradation of membrane phospholipids is associated with apoptotic responses, but the signaling development of this degradation is not well understood. Cerium (Ce(4+)), an important rare earth element, induces cellular apoptosis and taxol biosynthesis in Taxus cuspidata suspension cultures. Here, using mass spectrometry and biochemical technique, we demonstrated that the phospholipase D (PLD) was rapidly activated by Ce(4+) and hydrolyzed structural phospholipids to generate lipid signal molecule, phosphatidic acid (PA). 1-Butanol, an antagonist of PLD-dependent PA production, blocked the biphasic burst of superoxide anions (O2(*-)) and thus mitigated cellular apoptosis. The time-course analysis of PA accumulation and ERK-like mitogen-activated protein kinase (MAPK) regulation indicated PA generation preceded MAPK activation, suggesting that the rapid accumulation of PA might be required for the initial MAPK activity. After 2h of Ce(4+) elicitation, however, PA-induced O2(*-) burst, forming a negative regulation to MAPK activity, which in turn led to apoptotic signaling development.

The involvement of phospholipases C and D in the asymmetric division of subsidiary cell mother cells of Zea mays

In the present study, the involvement of phospholipase C and D (PLC and PLD) pathways in the asymmetric divisions that produce the stomatal complexes of Zea mays was investigated. In particular, the polar organization of microtubules (MTs) and actin filaments (AFs) and the process of asymmetric division were studied in subsidiary cell mother cells (SMCs) treated with PLC and PLD modulators. In SMCs treated with butanol-1 (but-1), which blocks phosphatidic acid (PA) production via PLDs, AF-patch formation laterally to the inducing guard cell mother cell (GMC) and the subsequent asymmetric division were inhibited. In these SMCs, cell division plane determination, as expressed by MT preprophase band (MT-PPB) formation, was not disturbed. Exogenously applied PA partially relieved the but-1 effects on SMCs. In contrast to SMCs, but-1 did not affect the symmetric GMC division. Inhibition of the PLC catalytic activity by neomycin or U73122 resulted in inhibition of asymmetric SMC division, while AF-patch and MT-PPB were organized as in control SMCs. These data show that the PLC and PLD signaling pathways are involved in the transduction and/or perception of the inductive stimulus that is emitted by the GMCs and induces the polar AF organization and asymmetric SMC division. In contrast, division plane determination in SMCs, as expressed by MT-PPB formation, does not depend on PLC and PLD signaling pathways.

Overexpression of a fatty acid amide hydrolase compromises innate immunity in Arabidopsis

N-acylethanolamines are a group of lipid mediators that accumulate under a variety of neurological and pathological conditions in mammals. N-acylethanolamine signaling is terminated by the action of diverse hydrolases, among which fatty acid amide hydrolase (FAAH) has been well characterized. Here, we show that transgenic Arabidopsis lines overexpressing an AtFAAH are more susceptible to the bacterial pathogens Pseudomonas syringae pv. tomato and P. syringae pv. maculicola. AtFAAH overexpressors also were highly susceptible to non-host pathogens P. syringae pv. syringae and P. syringae pv. tabaci. AtFAAH overexpressors had lower amounts of jasmonic acid, abscisic acid and both free and conjugated salicylic acid (SA), compared with the wild-type. Gene expression studies revealed that transcripts of a number of plant defense genes, as well as genes involved in SA biosynthesis and signaling, were lower in AtFAAH overexpressors than wild-type plants. Our data suggest that FAAH overexpression alters phytohormone accumulation and signaling which in turn compromises innate immunity to bacterial pathogens.

Enhanced induction of microspore embryogenesis after n-butanol treatment in wheat (Triticum aestivum L.) anther culture

The aim of this study was the improvement of embryo production in wheat anther culture. Three butanol alcohols, n-butanol, sec-butanol and tert-butanol, were evaluated for their effect on microspore embryogenesis in two spring cultivars of wheat, Pavon and Caramba. Application of n-butanol, at 0.1 and 0.2% (v/v) in the induction media for 5 h, highly improved embryo production in both cultivars. Sec- and tert-butanol performed similarly to control plates. Regeneration ability was unaffected by any butyl-alcohol treatment. As a consequence of the higher embryo production after n-butanol treatment, the number of green regenerated plants increased up to five times in cultivar Pavon and up to three times in cultivar Caramba. The percentage of green plants was improved or unaffected by the treatment. Doubled haploid plant production was between 2 and 4 times higher after n-butanol treatment than in control plates. Therefore, n-butanol was successfully applied in the production of wheat doubled haploids. This primary alcohol is known as an activator of phospholipase D and has been previously reported to disrupt cortical microtubules and detach them from the plasma membrane in plants. Its effects on androgenetic induction could confirm the importance of microtubule regulation in plant cell fate, specifically in microspore development. A possible implication of phospholipase D is discussed.

Phospholipase C signaling involvement in macrotubule assembly and activation of the mechanism regulating protoplast volume in plasmolyzed root cells of Triticum turgidum

The role of phosphoinositide-specific phospholipase C (PI-PLC) signaling in the macrotubule-dependent protoplast volume regulation in plasmolyzed root cells of Triticum turgidum was investigated. At the onset of hyperosmotic stress, PI-PLC activation was documented. Inhibition of PI-PLC activity by U73122 blocked tubulin macrotubule formation in plasmolyzed cells and their protoplast volume regulatory mechanism. In neomycin-treated plasmolyzed cells, macrotubule formation and protoplast volume regulation were not affected. In these cells the PI-PLC pathway is down-regulated as neomycin sequesters the PI-PLC substrate, 4,5-diphosphate-phosphatidyl inositol (PtdInsP(2)). These phenomena were unaffected by R59022, an inhibitor of phosphatidic acic (PA) production via the PLC pathway. Taxol, a microtubule (MT) stabilizer, inhibited the hyperosmotic activation of PI-PLC, but oryzalin, which disorganized MTs, triggered PI-PLC activity. Taxol prevented macrotubule formation and inhibited the mechanism regulating the volume of the plasmolyzed protoplast. Neomycin partly relieved some of the taxol effects. These data suggest that PtdInspP(2) turnover via PI-PLC assists macrotubule formation and activation of the mechanism regulating the plasmolyzed protoplast volume; and the massive disorganization of MTs that is carried out at the onset of hyperosmotic treatment triggers the activation of this mechanism.

TheN-Acylethanolamine-Mediated Regulatory Pathway in Plants

While cannabinoids are secondary metabolites synthesized by just a few plant species, N-acylethanolamines (NAEs) are distributed widely in the plant kingdom, and are recovered in measurable, bioactive quantities in many plant-derived products. NAEs in higher plants are ethanolamides of fatty acids with acyl-chain lenghts of C12-C(18) and zero to three C=C bonds. Generally, the most-abundant NAEs found in plants and vertebrates are similar, including NAE 16 : 0, 18 : 1, 18 : 2, and 18 : 3. Like in animal systems, NAEs are formed in plants from N-acylphosphatidylethanolamines (NAPEs), and they are hydrolyzed by an amidase to yield ethanolamine and free fatty acids (FFA). Recently, a homologue of the mammalian fatty acid amide hydrolase (FAAH-1) was identified in Arabidopsis thaliana and several other plant species. Overexpression of Arabidopsis FAAH (AtFAAH) resulted in plants that grew faster, but were more sensitive to biotic and abiotic insults, suggesting that the metabolism of NAEs in plants resides at the balance between growth and responses to environmental stresses. Similar to animal systems, exogenously applied NAEs have potent and varied effects on plant cells. Recent pharmacological approaches combined with molecular-genetic experiments revealed that NAEs may act in certain plant tissues via specific membrane-associated proteins or by interacting with phospholipase D-alpha, although other, direct targets for NAE action in plants are likely to be discovered. Polyunsaturated NAEs can be oxidized via the lipoxygenase pathway in plants, producing an array of oxylipin products that have received little attention so far. Overall, the conservation of NAE occurrence and metabolic machinery in plants, coupled with the profound physiological effects of elevating NAE content or perturbing endogenous NAE metabolism, suggest that an NAE-mediated regulatory pathway, sharing similarities with the mammalian endocannabinoid pathway, indeed exists.

N-Acylethanolamine metabolism interacts with abscisic acid signaling in Arabidopsis thaliana seedlings

N-Acylethanolamines (NAEs) are bioactive acylamides that are present in a wide range of organisms. In plants, NAEs are generally elevated in desiccated seeds, suggesting that they may play a role in seed physiology. NAE and abscisic acid (ABA) levels were depleted during seed germination, and both metabolites inhibited the growth of Arabidopsis thaliana seedlings within a similar developmental window. Combined application of low levels of ABA and NAE produced a more dramatic reduction in germination and growth than either compound alone. Transcript profiling and gene expression studies in NAE-treated seedlings revealed elevated transcripts for a number of ABA-responsive genes and genes typically enriched in desiccated seeds. The levels of ABI3 transcripts were inversely associated with NAE-modulated growth. Overexpression of the Arabidopsis NAE degrading enzyme fatty acid amide hydrolase resulted in seedlings that were hypersensitive to ABA, whereas the ABA-insensitive mutants, abi1-1, abi2-1, and abi3-1, exhibited reduced sensitivity to NAE. Collectively, our data indicate that an intact ABA signaling pathway is required for NAE action and that NAE may intersect the ABA pathway downstream from ABA. We propose that NAE metabolism interacts with ABA in the negative regulation of seedling development and that normal seedling establishment depends on the reduction of the endogenous levels of both metabolites.